1. Field of the Invention
The present invention relates to hot-fillable containers. More particularly, the present invention relates to hot-fillable containers having vacuum panels.
2. Statement of the Prior Art
The use of blow molded plastic containers for packaging “hot-fill” beverages is well known. However, a container that is used for hot-fill applications is subject to additional mechanical stresses on the container that result in the container being more likely to fail during storage or handling. For example, it has been found that the thin sidewalls of the container deform or collapse as the container is being filled with hot fluids. In addition, the rigidity of the container decreases immediately after the hot-fill liquid is introduced into the container. As the liquid cools, the liquid shrinks in volume, which, in turn, produces a negative pressure or vacuum in the container. The container must be able to withstand such changes in pressure without failure.
Hot-fill containers typically comprise substantially rectangular vacuum panels that are designed to collapse inwardly after the container has been filled with hot liquid. However, the inward flexing of the panels caused by the hot-fill vacuum creates high stress points at the top and bottom edges of the vacuum panels, especially at the upper and lower corners of the panels. These stress points weaken the portions of the sidewall near the edges of the panels, allowing the sidewall to collapse inwardly during handling of the container or when containers are stacked together. See, for example, U.S. Pat. No. 5,337,909.
The presence of annular reinforcement ribs that extend continuously around the circumference of the container sidewall are shown in U.S. Pat. No. 5,337,909. These ribs are indicated as supporting the vacuum panels at their upper and lower edges. This holds the edges fixed, while permitting the center portions of the vacuum panels to flex inwardly while the bottle is being filled. These ribs also resist the deformation of the vacuum panels. The reinforcement ribs can merge with the edges of the vacuum panels at the edge of the label upper and lower mounting panels.
Another hot-fill container having reinforcement ribs is disclosed in WO 97/34808. The container comprises a label mounting area having an upper and lower series of peripherally spaced, short, horizontal ribs separated endwise by label mount areas. It is stated that each upper and lower rib is located within the label mount section and is centered above or below, respectively, one of the lands. The container further comprises several rectangular vacuum panels that also experience high stress point at the corners of the collapse panels. These ribs stiffen the container adjacent lower corners of the collapse panels.
Stretch blow molded containers such as hot-filled PET juice containers, must be able to maintain their function, shape and labelability on cool down to room temperature or refrigeration. In the case of non-round containers, this is more challenging due to the fact that the level of orientation and, therefore, crystallinity is inherently lower in the front and back than on the narrower sides. Since the front and back are normally where vacuum panels are located, these areas must be made thicker to compensate for their relatively lower strength.